Electrolytes containing six membered ring cyclic sulfates

ABSTRACT

Disclosed herein are electrolyte compositions comprising at least one electrolyte component comprising a cyclic carbonate, such as a fluoroethylene carbonate, and at least one additive comprising a 6-member ring heterocyclic sulfate, such as a 1,3 propylene sulfate. The disclosed electrolyte compositions can comprise additional electrolyte components, such as fluorinated acyclic carboxylic acid esters, and additional additives, such as lithium boron compounds, and cyclic carboxylic acid anhydrides, such as maleic anhydride. The improved battery performances, which include high temperature cycling conditions and/or room temperature stability, make these electrolyte compositions useful in electrochemical cells, such as lithium ion batteries.

FIELD OF DISCLOSURE

The disclosure herein relates to electrolyte compositions comprising atleast one electrolyte component comprising a cyclic carbonate, such as afluoroethylene carbonate, and at least one additive comprising a6-member ring heterocyclic sulfate, such as a 1,3 propylene sulfate. Theimproved battery performances, including high temperature cyclingconditions and/or room temperature stability, make these electrolytecompositions useful in electrochemical cells, such as lithium ionbatteries.

BACKGROUND

Batteries containing electrodes made from alkali metals, alkaline earthmetals, or compounds comprising these metals—for example lithium ionbatteries—typically incorporate electrolytes, additives and non-aqueoussolvents for the electrolytes used in the batteries. Additives canenhance the performance and safety of the battery, and therefore asuitable solvent must dissolve the electrolyte as well as the additives.The solvent must also be stable under the conditions prevalent in anactive battery system.

Electrolyte solvents used in lithium ion batteries typically incorporateorganic carbonate compounds or mixtures, and typically include one ormore linear carbonates such as, for example, ethyl methyl carbonate,dimethyl carbonate, or diethyl carbonate. Cyclic carbonates, such asethylene carbonate, can also be included. However, at cathode potentialsabove about 4.35 V these electrolyte solvents can decompose, which canresult in a loss of battery performance.

As a result of these problems, some lithium ion batteries which utilizea graphite anode or an anode composite (e.g. containing Si) containelectrolyte formulations with specific organic additives thatparticipate in reactions to form passivating or solid electrolyteinterphase layers (SEI's) on the electrode surfaces. These layers areideally electrically insulating but ionically conducting, and helpprevent decomposition of the electrolyte, thereby extending the cyclelife and improving the performance of the battery at low and hightemperatures. On the anode electrode, the SEI can suppress the reductivedecomposition of the electrolyte, whereas on the cathode electrode, theSEI can suppress the oxidation of the electrolyte components.

Specific organic additives, however, have been correlated with unwantedreactions of the electrolyte components leading to decreased roomtemperature stability and increased aging of the formulation. Thus,there remains a need for electrolyte solvent formulations that will haveimproved battery performance during high temperature cycling conditionsand improved room temperature storage and stability of the electrolyte.The stability of the electrolyte formulation at room temperature is animportant requirement for commercialization.

SUMMARY

In one aspect, there is provided an electrolyte composition comprising:

an electrolyte composition comprising:

at least one electrolyte component comprising a cyclic carbonate;

at least one additive comprising a 6-member ring heterocyclic sulfaterepresented by Formula (I):

wherein n=1, and R¹⁵ to R¹⁸ each independently represent a hydrogen or avinyl (H₂C═CH—), allyl (H₂C═CH—CH₂—), acetylenic (HC≡C—), propargyl(HC≡C—CH₂—), or C₁-C₃ alkyl group, wherein the vinyl, allyl, acetylenic,propargyl, or C₁-C₃ alkyl groups may each be unsubstituted or partiallyor totally fluorinated; and

at least one electrolyte salt.

In another embodiment, there is disclosed an electrochemical cellcomprising:

(a) a housing;

(b) an anode and a cathode disposed in the housing and in ionicallyconductive contact with one another;

(c) the electrolyte composition comprising:

-   -   at least one electrolyte component comprising a cyclic        carbonate; and    -   at least one additive comprising a 6-member ring heterocyclic        sulfate represented by Formula (I):

wherein n=1, and R¹⁵ to R¹⁸ each independently represent a hydrogen or avinyl (H₂C═CH—), allyl (H₂C═CH—CH₂—), acetylenic (HC≡C—), propargyl(HC≡C—CH₂—), or C₁-C₃ alkyl group, wherein the vinyl, allyl, acetylenic,propargyl, or C₁-C₃ alkyl groups may each be unsubstituted or partiallyor totally fluorinated; and

-   -   at least one electrolyte salt.

Other aspects of the disclosed invention may be inherent or understoodfrom the disclosure provided herein even though not specificallydescribed with particularity or completely embodied in a single exampleof this application, but which may nonetheless be synthesized by one ofordinary skill in the art from the totality of the description, theexamples, and the claims provided in the present application, that is,the whole of this specification.

As used above and throughout the disclosure, the following terms, unlessotherwise indicated, shall be defined as follows:

The term “electrolyte composition” as used herein, refers to a chemicalcomposition that includes—at a minimum—a solvent for an electrolyte saltand an electrolyte salt, wherein the composition is capable of supplyingan electrolyte in an electrochemical cell. An electrolyte compositioncan include other components, for example additives to enhance theperformance of the battery in safety, reliability, and or efficiency.

The term “electrolyte salt” as used herein, refers to an ionic salt thatis at least partially soluble in the solvent of the electrolytecomposition and that at least partially dissociates into ions in thesolvent of the electrolyte composition to form a conductive electrolytecomposition.

An “electrolyte solvent” as defined herein is a solvent or a solventmixture for an electrolyte composition that comprises a fluorinatedsolvent.

The term “anode” refers to the electrode of an electrochemical cell, atwhich oxidation occurs. In a secondary (i.e. rechargeable) battery, theanode is the electrode at which oxidation occurs during discharge andreduction occurs during charging.

The term “cathode” refers to the electrode of an electrochemical cell,at which reduction occurs. In a secondary (i.e. rechargeable) battery,the cathode is the electrode at which reduction occurs during dischargeand oxidation occurs during charging.

The term “lithium ion battery” refers to a type of rechargeable batteryin which lithium ions move from the anode to the cathode duringdischarge and from the cathode to the anode during charge.

The equilibrium potential between lithium and lithium ion is thepotential of a reference electrode using lithium metal in contact withthe non-aqueous electrolyte containing lithium salt at a concentrationsufficient to give about 1 mole/liter of lithium ion concentration, andsubjected to sufficiently small currents so that the potential of thereference electrode is not significantly altered from its equilibriumvalue (Li/Li⁺). The potential of such a Li/Li⁺ reference electrode isassigned here the value of 0.0 V. Potential of an anode or cathode meansthe potential difference between the anode or cathode and that of aLi/Li⁺ reference electrode. Herein voltage means the voltage differencebetween the cathode and the anode of a cell, neither electrode of whichmay be operating at a potential of 0.0 V.

An energy storage device is a device that is designed to provideelectrical energy on demand, such as a battery or a capacitor. Energystorage devices contemplated herein at least in part provide energy fromelectrochemical sources.

The term “SEI”, as used herein, refers to a solid electrolyte interphaselayer formed on the active material of an electrode. A lithium-ionsecondary electrochemical cell is assembled in an uncharged state andmust be charged (a process called formation) for use. During the firstfew charging events (battery formation) of a lithium-ion secondaryelectrochemical cell, components of the electrolyte are reduced orotherwise decomposed or incorporated onto the surface of the negativeactive material and oxidized or otherwise decomposed or incorporatedonto the surface of the positive active material, electrochemicallyforming a solid-electrolyte interphase on the active materials. Theselayers, which are electrically insulating but ionically conducting, helpprevent decomposition of the electrolyte and can extend the cycle lifeand improve the performance of the battery. On the anode, the SEI cansuppress the reductive decomposition of the electrolyte; on the cathode,the SEI can suppress the oxidation of the electrolyte components.

The term “alkyl group”, as used herein, refers to linear, branched, andcyclic hydrocarbon groups containing from 1 to 20 carbons and containingno unsaturation. Examples of straight chain alkyl radicals includemethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, and dodecyl. Examples of branched chain isomers ofstraight chain alkyl groups include isopropyl, iso-butyl, tert-butyl,sec-butyl, isopentyl, neopentyl, isohexyl, neohexyl, and isooctyl.Examples of cyclic alkyl groups include cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl.

The term “fluoroalkyl group”, as used herein, refers to an alkyl groupwherein at least one hydrogen is replaced by fluorine.

The term “carbonate” as used herein refers specifically to an organiccarbonate, wherein the organic carbonate is a dialkyl diester derivativeof carbonic acid, the organic carbonate having a general formulaR^(a)OCOOR^(b), wherein R^(a) and R^(b) are each independently selectedfrom alkyl groups having at least one carbon atom, wherein the alkylsubstituents can be the same or different, can be saturated orunsaturated, substituted or unsubstituted, can form a cyclic structurevia interconnected atoms, or include a cyclic structure as a substituentof either or both of the alkyl groups.

The phrase “taken as a pair” refers to the total number of the elementsin the combination that is being described. For example, the phrase “R¹and R², taken as a pair comprise at least two carbon atoms but not morethan seven carbon atoms” means the total number of carbon atoms in R¹and R² are at least two, not that each of R¹ and R² have at least 2carbon atoms.

There is disclosed electrolyte compositions comprising at least oneelectrolyte component comprising a cyclic carbonate, such as afluoroethylene carbonate, and at least one additive comprising a6-member ring heterocyclic sulfate, such as a 1,3 propylene sulfate. Thedisclosed electrolyte compositions have been shown to improve batteryperformance, including high temperature cycling conditions and/or roomtemperature stability, make these electrolyte compositions useful inelectrochemical cells, such as lithium ion batteries.

In one aspect, there is provided an electrolyte composition comprising:

an electrolyte composition comprising:

at least one electrolyte component comprising a cyclic carbonate;

at least one additive comprising a 6-member ring heterocyclic sulfaterepresented by Formula (I):

wherein R¹⁵ to R¹⁸ each independently represent a hydrogen or anoptionally fluorinated vinyl (H₂C═CH—), allyl (H₂C═CH—CH₂—), acetylenic(HC≡C—), propargyl (HC≡C—CH₂—), or C₁-C₃ alkyl group, wherein the vinyl,allyl, acetylenic, propargyl, or C₁-C₃ alkyl groups may each beunsubstituted or partially or totally fluorinated; and

at least one electrolyte salt.

In one embodiment, the disclosed electrolyte composition can include oneor more six-membered ring heterocyclic sulfate represented by Formula(I):

R¹⁵ to R¹⁸ each independently represent a hydrogen or an optionallyfluorinated vinyl, allyl, acetylenic, propargyl, or C₁-C₃ alkyl group,wherein the vinyl, allyl, acetylenic, propargyl, or C₁-C₃ alkyl groupsmay each be unsubstituted or partially or totally fluorinated; and n is1.

An example of a suitable heterocyclic sulfate is 1,3-propylene sulfate,in n=1 and each of R¹⁵, R¹⁶, R¹⁷, and R¹⁸ is H.

In one embodiment, the heterocyclic sulfate is present at about 0.1weight percent to about 12 weight percent of the total electrolytecomposition, or about 0.5 weight percent to less than about 10 weightpercent, about 0.5 weight percent to less than about 5 weight percent,or about 0.5 weight percent to about 3 weight percent, or about 1.0weight percent to about 2 weight percent. In one embodiment theheterocyclic sulfate is present at about 1 weight percent to about 3weight percent or about 1.5 weight percent to about 2.5 weight percent,or about 2 weight percent of the total electrolyte composition.

In one embodiment, the disclosed electrolyte composition can include oneor more cyclic carbonates. The cyclic carbonate can be fluorinated ornon-fluorinated. Suitable cyclic carbonates include, for example,ethylene carbonate; propylene carbonate; vinylene carbonate; vinylethylene carbonate; dimethylvinylene carbonate; ethyl propyl vinylenecarbonate; 4-fluoroethylene carbonate; 4,5-difluoro-1,3-dioxolan-2-one;4,5-difluoro-4-methyl-1,3-dioxolan-2-one;4,5-difluoro-4,5-dimethyl-1,3-dioxolan-2-one;4,4-difluoro-1,3-dioxolan-2-one; 4,4,5-trifluoro-1,3-dioxolan-2-one;tetrafluoroethylene carbonate; and mixtures thereof. 4-Fluoroethylenecarbonate is also known as 4-fluoro-1,3-dioxolan-2-one or fluoroethylenecarbonate. In one embodiment, the cyclic carbonate comprises ethylenecarbonate; propylene carbonate; vinylene carbonate; vinyl ethylenecarbonate; dimethylvinylene carbonate; ethyl propyl vinylene carbonate;4-fluoroethylene carbonate; 4,5-difluoro-1,3-dioxolan-2-one;4,5-difluoro-4-methyl-1,3-dioxolan-2-one;4,5-difluoro-4,5-dimethyl-1,3-dioxolan-2-one;4,4-difluoro-1,3-dioxolan-2-one; or 4,4,5-trifluoro-1,3-dioxolan-2-one.In one embodiment, the cyclic carbonate comprises ethylene carbonate. Inone embodiment, the cyclic carbonate comprises propylene carbonate. Inone embodiment, the cyclic carbonate comprises fluoroethylene carbonate.In one embodiment, the cyclic carbonate comprises vinylene carbonate. Itis desirable to use as a first solvent a cyclic carbonate that isbattery grade in purity, or has a purity level of at least about 99.9%,and more particularly at least about 99.99%. Such cyclic carbonates aretypically commercially available.

In one embodiment, the disclosed electrolyte composition can include oneor more non-fluorinated acyclic carbonates. Suitable non-fluorinatedacyclic carbonates include, for example, dimethyl carbonate, diethylcarbonate, dipropyl carbonate, dibutyl carbonate, di-tert-butylcarbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl butylcarbonate, ethyl propyl carbonate, ethyl butyl carbonate, propyl butylcarbonate, or mixtures thereof. In one embodiment, the non-fluorinatedacyclic carbonate comprises dimethyl carbonate, diethyl carbonate,dipropyl carbonate, dibutyl carbonate, or ethyl methyl carbonate. In oneembodiment, the non-fluorinated acyclic carbonate comprises dimethylcarbonate. In one embodiment, the non-fluorinated acyclic carbonatecomprises diethyl carbonate. In one embodiment, the non-fluorinatedacyclic carbonate comprises ethyl methyl carbonate. It is desirable touse as a second solvent a non-fluorinated acyclic carbonate that isbattery grade in purity, or has a purity level of at least about 99.9%,and more particularly at least about 99.99%. Such non-fluorinatedacyclic carbonates are typically commercially available.

The electrolyte compositions disclosed herein also comprise at least oneelectrolyte component selected from a fluorinated acyclic carboxylicacid ester, a fluorinated acyclic carbonate, a fluorinated acyclicether, or a mixture thereof.

Without being bound by any theory, it is thought that the use ofelectrolyte components as disclosed herein in the electrolytecompositions disclosed herein can, after electrochemical cycling, modifythe composition of the solid electrolyte interphase (SEI) layer formedon the active material of an electrode. This modification may have abeneficial impact on the performance of the battery and its cycle lifedurability.

In one embodiment, the at least one electrolyte component comprises afluorinated acyclic carboxylic acid ester represented by the formula:R¹—COO—R²wherein

i) R¹ is H, an alkyl group, or a fluoroalkyl group;

ii) R² is an alkyl group or a fluoroalkyl group;

iii) either or both of R¹ and R² comprises fluorine; and

iv) R¹ and R², taken as a pair, comprise at least two carbon atoms butnot more than seven carbon atoms.

In one embodiment, R¹ is H and R² is a fluoroalkyl group. In oneembodiment, R¹ is an alkyl group and R² is a fluoroalkyl group. In oneembodiment, R¹ is a fluoroalkyl group and R² is an alkyl group. In oneembodiment, R¹ is a fluoroalkyl group and R² is a fluoroalkyl group, andR¹ and R² can be either the same as or different from each other. In oneembodiment, R¹ comprises one carbon atom. In one embodiment, R¹comprises two carbon atoms.

In another embodiment, R¹ and R² are as defined herein above, and R¹ andR², taken as a pair, comprise at least two carbon atoms but not morethan seven carbon atoms and further comprise at least two fluorineatoms, with the proviso that neither R¹ nor R² contains a FCH₂— group ora —FCH— group.

In one embodiment, the number of carbon atoms in R¹ in the formula aboveis 1, 3, 4, or 5.

In another embodiment, the number of carbon atoms in R¹ in the formulaabove is 1.

Examples of suitable fluorinated acyclic carboxylic acid esters includewithout limitation CH₃—COO—CH₂CF₂H (2,2-difluoroethyl acetate, CAS No.1550-44-3), CH₃—COO—CH₂CF₃ (2,2,2-trifluoroethyl acetate, CAS No.406-95-1), CH₃CH₂—COO—CH₂CF₂H (2,2-difluoroethyl propionate, CAS No.1133129-90-4), CH₃—COO—CH₂CH₂CF₂H (3,3-difluoropropyl acetate),CH₃CH₂—COO—CH₂CH₂CF₂H (3,3-difluoropropyl propionate), F₂CHCH₂—COO—CH₃,F₂CHCH₂—COO—CH₂CH₃, and F₂CHCH₂CH₂—COO—CH₂CH₃ (ethyl4,4-difluorobutanoate, CAS No. 1240725-43-2), H—COO—CH₂CF₂H(difluoroethyl formate, CAS No. 1137875-58-1), H—COO—CH₂CF₃(trifluoroethyl formate, CAS No. 32042-38-9), and mixtures thereof. Inone embodiment, the fluorinated acyclic carboxylic acid ester comprises2,2-difluoroethyl acetate (CH₃—COO—CH₂CF₂H). In one embodiment, thefluorinated acyclic carboxylic acid ester comprises 2,2-difluoroethylpropionate (CH₃CH₂—COO—CH₂CF₂H). In one embodiment, the fluorinatedacyclic carboxylic acid ester comprises 2,2,2-trifluoroethyl acetate(CH₃—COO—CH₂CF₃). In one embodiment, the fluorinated acyclic carboxylicacid ester comprises 2,2-difluoroethyl formate (H—COO—CH₂CF₂H).

In one embodiment, the fluorinated acyclic carboxylic acid estercomprises CH₃—COO—CH₂CF₂H, and the electrolyte composition furthercomprises lithium bis(oxalato)borate, ethylene sulfate, and maleicanhydride.

In another embodiment, the at least one electrolyte component is afluorinated acyclic carbonate represented by the formulaR³—OCOO—R⁴wherein

i) R³ is a fluoroalkyl group;

ii) R⁴ is an alkyl group or a fluoroalkyl group; and

iii) R³ and R⁴ taken as a pair comprise at least two carbon atoms butnot more than seven carbon atoms.

In one embodiment, R³ is a fluoroalkyl group and R⁴ is an alkyl group.In one embodiment, R³ is a fluoroalkyl group and R⁴ is a fluoroalkylgroup, and R³ and R⁴ can be either the same as or different from eachother. In one embodiment, R³ comprises one carbon atom. In oneembodiment, R³ comprises two carbon atoms.

In another embodiment, R³ and R⁴ are as defined herein above, and R³ andR⁴, taken as a pair, comprise at least two carbon atoms but not morethan seven carbon atoms and further comprise at least two fluorineatoms, with the proviso that neither R³ nor R⁴ contains a FCH₂— group ora —FCH— group.

Examples of suitable fluorinated acyclic carbonates include withoutlimitation CH₃—OC(O)O—CH₂CF₂H (methyl 2,2-difluoroethyl carbonate, CASNo. 916678-13-2), CH₃—OC(O)O—CH₂CF₃ (methyl 2,2,2-trifluoroethylcarbonate, CAS No. 156783-95-8), CH₃—OC(O)O—CH₂CF₂CF₂H (methyl2,2,3,3-tetrafluoropropyl carbonate, CAS No. 156783-98-1),HCF₂CH₂—OCOO—CH₂CH₃ (ethyl 2,2-difluoroethyl carbonate, CAS No.916678-14-3), and CF₃CH₂—OCOO—CH₂CH₃ (ethyl 2,2,2-trifluoroethylcarbonate, CAS No. 156783-96-9).

In another embodiment, the at least one electrolyte component is afluorinated acyclic ether represented by the formulaR⁵—O—R⁶wherein

i) R⁵ is a fluoroalkyl group;

ii) R⁶ is an alkyl group or a fluoroalkyl group; and

iii) R⁵ and R⁶ taken as a pair comprise at least two carbon atoms butnot more than seven carbon atoms.

In one embodiment, R⁵ is a fluoroalkyl group and R⁶ is an alkyl group.In one embodiment, R⁵ is a fluoroalkyl group and R⁶ is a fluoroalkylgroup, and R⁵ and R⁶ can be either the same as or different from eachother. In one embodiment, R⁵ comprises one carbon atom. In oneembodiment, R⁵ comprises two carbon atoms.

In another embodiment, R⁵ and R⁶ are as defined herein above, and R⁵ andR⁶, taken as a pair, comprise at least two carbon atoms but not morethan seven carbon atoms and further comprise at least two fluorineatoms, with the proviso that neither R⁵ nor R⁶ contains a FCH₂— group ora —FCH— group.

Examples of suitable fluorinated acyclic ethers include withoutlimitation HCF₂CF₂CH₂—O—CF₂CF₂H (CAS No. 16627-68-2) andHCF₂CH₂—O—CF₂CF₂H (CAS No. 50807-77-7).

In another embodiment, the electrolyte component is a mixture comprisinga fluorinated acyclic carboxylic acid ester, a fluorinated acycliccarbonate, and/or a fluorinated acyclic ether. As used herein, the term“a mixture thereof” encompasses both mixtures within and mixturesbetween solvent classes, for example mixtures of two or more fluorinatedacyclic carboxylic acid esters, and also mixtures of fluorinated acycliccarboxylic acid esters and fluorinated acyclic carbonates, for example.Non-limiting examples include a mixture of 2,2-difluoroethyl acetate and2,2-difluoroethyl propionate; and a mixture of 2,2-difluoroethyl acetateand 2,2 difluoroethyl methyl carbonate.

Fluorinated acyclic carboxylic acid esters, fluorinated acycliccarbonates, and fluorinated acyclic ethers suitable for use herein maybe prepared using known methods.

For example, acetyl chloride may be reacted with 2,2-difluoroethanol(with or without a basic catalyst) to form 2,2-difluoroethyl acetate.Additionally, 2,2-difluoroethyl acetate and 2,2-difluoroethyl propionatemay be prepared using the method described by Wiesenhofer et al. (WO2009/040367 A1, Example 5). Alternatively, 2,2-difluoroethyl acetate canbe prepared using the method described in the Examples herein below.Other fluorinated acyclic carboxylic acid esters may be prepared usingthe same method using different starting carboxylate salts. Similarly,methyl chloroformate may be reacted with 2,2-difluoroethanol to formmethyl 2,2-difluoroethyl carbonate. Synthesis of HCF₂CF₂CH₂—O—CF₂CF₂Hcan be done by reacting 2,2,3,3-tetrafluoropropanol withtetrafluoroethylene in the presence of base (e.g., NaH, etc.).Similarly, reaction of 2,2-difluoroethanol with tetrafluoroethyleneyields HCF₂CH₂—O—CF₂CF₂H. Alternatively, some of these fluorinatedelectrolyte components may be obtained commercially. It is desirable topurify the electrolyte component to a purity level of at least about99.9%, more particularly at least about 99.99%, for use in anelectrolyte composition. Purification may be performed usingdistillation methods such as vacuum distillation or spinning banddistillation.

The electrolyte compositions disclosed herein also comprise anelectrolyte salt. Suitable electrolyte salts include without limitation:

lithium hexafluorophosphate (LiPF₆),

lithium difluorophosphate (LiPO₂F₂),

lithium bis(trifluoromethyl)tetrafluorophosphate (LiPF₄(CF₃)₂),

lithium bis(pentafluoroethyl)tetrafluorophosphate (LiPF₄(C₂F₅)₂),

lithium tris(pentafluoroethyl)trifluorophosphate (LiPF₃(C₂F₅)₃),

lithium bis(trifluoromethanesulfonyl)imide,

lithium bis(perfluoroethanesulfonyl)imide,

lithium (fluorosulfonyl) (nonafluorobutanesulfonyl)imide,

lithium bis(fluorosulfonyl)imide,

lithium tetrafluoroborate,

lithium perchlorate,

lithium hexafluoroarsenate,

lithium trifluoromethanesulfonate,

lithium tris(trifluoromethanesulfonyl)methide,

lithium bis(oxalato)borate,

lithium difluoro(oxalato)borate,

Li₂B₁₂F_(12-x)H_(x) where x is equal to 0 to 8, and

mixtures of lithium fluoride and anion receptors such as B(OC₆F₅)₃.

Mixtures of two or more of these or comparable electrolyte salts mayalso be used.

In one embodiment, the electrolyte salt comprises lithiumbis(trifluoromethanesulfonyl)imide. In one embodiment, the electrolytesalt comprises lithium hexafluorophosphate. The electrolyte salt can bepresent in the electrolyte composition in an amount from about 0.2 M toabout 2.0 M, for example from about 0.3 M to about 1.7 M, or for examplefrom about 0.5 M to about 1.2 M, or for example 0.5 M to about 1.7M.

Optionally, an electrolyte composition as described herein may furthercomprise an additive selected from a lithium boron compound, a cyclicsultone, a cyclic sulfate, a cyclic carboxylic acid anhydride, or acombination thereof. In some embodiments, the electrolyte compositionfurther comprises an additive selected from a lithium boron compound, acyclic sultone, a cyclic sulfate, a cyclic carboxylic acid anhydride, ora combination thereof, and the electrolyte component comprises afluorinated acyclic carboxylic acid ester represented by the formula:R¹—COO—R²,wherein

i) R¹ is H, an alkyl group, or a fluoroalkyl group;

ii) R² is an alkyl group or a fluoroalkyl group;

iv) either or both of R¹ and R² comprises fluorine; and

v) R¹ and R², taken as a pair, comprise at least two carbon atoms butnot more than seven carbon atoms. In some embodiments, the fluorinatedacyclic carboxylic acid ester comprises CH₃—COO—CH₂CF₂H.

In some embodiments, the electrolyte composition further comprises alithium boron compound. Suitable lithium boron compounds include lithiumtetrafluoroborate, lithium bis(oxalato)borate, lithiumdifluoro(oxalato)borate, other lithium boron salts, Li₂B₁₂F_(12-x)H_(x),wherein x is 0 to 8, mixtures of lithium fluoride and anion receptorssuch as B(OC₆F₅)₃, or mixtures thereof. In one embodiment, theelectrolyte composition additionally comprises at least one lithiumborate salt selected from lithium bis(oxalato)borate, lithiumdifluoro(oxalato)borate, lithium tetrafluoroborate, or mixtures thereof.In some embodiments, the electrolyte composition comprises lithiumbis(oxalato)borate. In some embodiments, the electrolyte compositioncomprises lithium difluoro(oxalato)borate. In some embodiments, theelectrolyte composition comprises lithium tetrafluoroborate. The lithiumborate salt may be present in the electrolyte composition in the rangeof from 0.1 to about 10 percent by weight, based on the total weight ofthe electrolyte composition, for example in the range of from 0.1 toabout 5.0 percent by weight, or from 0.3 to about 4.0 percent by weight,or from 0.5 to 2.0 percent by weight. The lithium boron compounds can beobtained commercially or prepared by methods known in the art.

In some embodiments, the electrolyte composition further comprises acyclic sultone. Suitable sultones include those represented by theformula:

wherein each A is independently a hydrogen, fluorine, or an optionallyfluorinated alkyl, vinyl, allyl, acetylenic, or propargyl group. Thevinyl (H₂C═CH—), allyl (H₂C═CH—CH₂—), acetylenic (HC≡C—), or propargyl(HC≡C—CH₂—) groups may each be unsubstituted or partially or totallyfluorinated. Each A can be the same or different as one or more of theother A groups, and two or three of the A groups can together form aring. Mixtures of two or more of sultones may also be used. Suitablesultones include 1,3-propane sultone, 3-fluoro-1,3-propane sultone,4-fluoro-1,3-propane sultone, 5-fluoro-1,3-propane sultone, and1,8-naphthalenesultone. In one embodiment, the sultone comprises1,3-propane sultone. In one embodiment, the sultone comprises3-fluoro-1,3-propane sultone.

In one embodiment, the sultone is present at about 0.01 to about 10weight percent, or about 0.1 weight percent to about 5 weight percent,or about 0.5 weight percent to about 3 weight percent, or about 1 weightpercent to about 3 weight percent or about 1.5 weight percent to about2.5 weight percent, or about 2 weight percent, of the total electrolytecomposition.

In some embodiments, the electrolyte composition further comprises acyclic carboxylic acid anhydride. Suitable cyclic carboxylic acidanhydrides include those selected from the group consisting of thecompounds represented by Formula (I) through Formula (VIII):

wherein R⁷ to R¹⁴ is each independently H, F, a linear or branched C₁ toC₁₀ alkyl radical optionally substituted with F, alkoxy, and/orthioalkyl substituents, a linear or branched C₂ to C₁₀ alkene radical,or a C₆ to C₁₀ aryl radical. The alkoxy substituents can have from oneto ten carbons and can be linear or branched; examples of alkoxysubstituents include —OCH₃, —OCH₂CH₃, and —OCH₂CH₂CH₃. The thioalkylsubstituents can have from one to ten carbons and can be linear orbranched; examples of thioalkyl substituents include —SCH₃, —SCH₂CH₃,and —SCH₂CH₂CH₃. Examples of suitable cyclic carboxylic acid anhydridesinclude maleic anhydride; succinic anhydride; glutaric anhydride;2,3-dimethylmaleic anhydride; citraconic anhydride;1-cyclopentene-1,2-dicarboxylic anhydride; 2,3-diphenylmaleic anhydride;3,4,5,6-tetrahydrophthalic anhydride; 2,3-dihydro-1,4-dithiiono-[2,3-c]furan-5,7-dione; and phenylmaleic anhydride. A mixture of two or more ofthese cyclic carboxylic acid anhydrides can also be used. In oneembodiment, the cyclic carboxylic acid anhydride comprises maleicanhydride. In one embodiment, the cyclic carboxylic acid anhydridecomprises maleic anhydride, succinic anhydride, glutaric anhydride,2,3-dimethylmaleic anhydride, citraconic anhydride, or mixtures thereof.Cyclic carboxylic acid anhydrides can be obtained from a specialtychemical company such as Sigma-Aldrich, Inc. (Milwaukee, Wis.), orprepared using methods known in the art. It is desirable to purify thecyclic carboxylic acid anhydride to a purity level of at least about99.0%, for example at least about 99.9%. Purification can be done usingmethods known in the art.

In some embodiments, the electrolyte composition comprises about 0.1weight percent to about 5 weight percent of the cyclic carboxylic acidanhydride, based on the total weight of the electrolyte composition. Insome embodiments, the cyclic carboxylic acid anhydride is present in theelectrolyte composition in a percentage by weight that is defined by alower limit and an upper limit. The lower limit of the range is 0.1,0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5,1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or 2.5 and the upper limitof the range is 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6,3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5.0.All percentages by weight are based on the total weight of theelectrolyte composition.

In some embodiments, the electrolyte composition further comprises aheterocyclic sulfate containing a higher than six-membered ring.Suitable heterocyclic sulfates include those compounds represented byFormula (I):

wherein R¹⁵ to R¹⁸ each independently represent hydrogen, halogen, a C₁to C₁₂ alkyl group, or a C₁ to C₁₂ fluoroalkyl group, and n has a valueof 2 or 3.

In one embodiment, R¹⁵ to R¹⁸ are independently a hydrogen or anoptionally fluorinated vinyl, allyl, acetylenic, propargyl, or C₁-C₃alkyl group. The vinyl (H₂C═CH—), allyl (H₂C═CH—CH₂—), acetylenic(HC≡C—), propargyl (HC≡C—CH₂—), or C₁-C₃ alkyl groups may each beunsubstituted or partially or totally fluorinated

In one embodiment, the heterocyclic sulfate is present at about 0.1weight percent to about 12 weight percent of the total electrolytecomposition, or about 0.5 weight percent to less than about 10 weightpercent, about 0.5 weight percent to less than about 5 weight percent,or about 0.5 weight percent to about 3 weight percent, or about 1.0weight percent to about 2 weight percent. In one embodiment theheterocyclic sulfate is present at about 1 weight percent to about 3weight percent or about 1.5 weight percent to about 2.5 weight percent,or about 2 weight percent of the total electrolyte composition.

Optionally, the electrolyte compositions disclosed herein can furthercomprise additives that are known to those of ordinary skill in the artto be useful in conventional electrolyte compositions, particularly foruse in lithium ion batteries. For example, electrolyte compositionsdisclosed herein can also include gas-reduction additives which areuseful for reducing the amount of gas generated during charging anddischarging of lithium ion batteries. Gas-reduction additives can beused in any effective amount, but can be included to comprise from about0.05 weight % to about 10 weight %, alternatively from about 0.05 weight% to about 5 weight % of the electrolyte composition, or alternativelyfrom about 0.5 weight % to about 2 weight % of the electrolytecomposition.

Suitable gas-reduction additives that are known conventionally are, forexample: halobenzenes such as fluorobenzene, chlorobenzene,bromobenzene, iodobenzene, or haloalkylbenzenes; 1,3-propane sultone;succinic anhydride; ethynyl sulfonyl benzene; 2-sulfobenzoic acid cyclicanhydride; divinyl sulfone; triphenylphosphate (TPP); diphenyl monobutylphosphate (DMP); γ-butyrolactone; 2,3-dichloro-1,4-naphthoquinone;1,2-naphthoquinone; 2,3-dibromo-1,4-naphthoquinone;3-bromo-1,2-naphthoquinone; 2-acetylfuran; 2-acetyl-5-methylfuran;2-methyl imidazolel-(phenylsulfonyl)pyrrole; 2,3-benzofuran;fluoro-cyclotriphosphazenes such as2,4,6-trifluoro-2-phenoxy-4,6-dipropoxy-cyclotriphosphazene and2,4,6-trifluoro-2-(3-(trifluoromethyl)phenoxy)-6-ethoxy-cyclotriphosphazene;benzotriazole; perfluoroethylene carbonate; anisole; diethylphosphonate;fluoroalkyl-substituted dioxolanes such as 2-trifluoromethyldioxolaneand 2,2-bistrifluoromethyl-1,3-dioxolane; trimethylene borate;dihydro-3-hydroxy-4,5,5-trimethyl-2(3H)-furanone;dihydro-2-methoxy-5,5-dimethyl-3(2H)-furanone;dihydro-5,5-dimethyl-2,3-furandione; propene sultone; diglycolic acidanhydride; di-2-propynyl oxalate; 4-hydroxy-3-pentenoic acid γ-lactone;CF₃COOCH₂C(CH₃)(CH₂OCOCF₃)₂; CF₃COOCH₂CF₂CF₂CF₂CF₂CH₂OCOCF₃;α-methylene-γ-butyrolactone; 3-methyl-2(5H)-furanone;5,6-dihydro-2-pyranone; diethylene glycol, diacetate; triethylene glycoldimethacrylate; triglycol diacetate; 1,2-ethanedisulfonic anhydride;1,3-propanedisulfonic anhydride; 2,2,7,7-tetraoxide 1,2,7-oxadithiepane;3-methyl-, 2,2,5,5-tetraoxide 1,2,5-oxadithiolane; hexamethoxycyclotriphosphazene; 4,5-dimethyl-4,5-difluoro-1,3-dioxolan-2-one;2-ethoxy-2,4,4,6,6-pentafluoro-2,2,4,4,6,6-hexahydro-1,3,5,2,4,6-triazatriphosphorine;2,2,4,4,6-pentafluoro-2,2,4,4,6,6-hexahydro-6-methoxy-1,3,5,2,4,6-triazatriphosphorine;4,5-Difluoro-1,3-dioxolan-2-one; 1,4-bis(ethenylsulfonyl)-butane;bis(vinylsulfonyl)-methane; 1,3-bis(ethenylsulfonyl)-propane;1,2-bis(ethenylsulfonyl)-ethane; ethylene carbonate; diethyl carbonate;dimethyl carbonate; ethyl methyl carbonate; and1,1′-[oxybis(methylenesulfonyl)]bis-ethene.

Other suitable additives that can be used are HF scavengers, such assilanes, silazanes (Si—NH—Si), epoxides, amines, aziridines (containingtwo carbons), salts of carbonic acid lithium oxalate, B₂O₅, ZnO, andfluorinated inorganic salts.

In another embodiment, there is provided herein an electrochemical cellcomprising a housing, an anode and a cathode disposed in the housing andin ionically conductive contact with one another, an electrolytecomposition as described herein above disposed in the housing andproviding an ionically conductive pathway between the anode and thecathode, and a porous separator between the anode and the cathode. Insome embodiments, the electrochemical cell is a lithium ion battery.

In some embodiments, the electrolyte component of the electrolytecomposition disposed in the housing comprises a fluorinated acycliccarboxylic acid ester, and the fluorinated acyclic carboxylic acid estercomprises CH₃—COO—CH₂CF₂H, CH₃CH₂—COO—CH₂CF₂H, F₂CHCH₂—COO—CH₃,F₂CHCH₂—COO—CH₂CH₃, CH₃—COO—CH₂CH₂CF₂H, CH₃CH₂—COO—CH₂CH₂CF₂H,F₂CHCH₂CH₂—COO—CH₂CH₃, CH₃—COO—CH₂CF₃, CH₃CH₂—COO—CH₂CF₂H,CH₃—COO—CH₂CF₃, H—COO—CH₂CF₂H, H—COO—CH₂CF₃, or mixtures thereof.

In some embodiments, the electrolyte component of the electrolytecomposition disposed in the housing comprises a fluorinated acycliccarbonate, and the fluorinated acyclic carbonate comprisesCH₃—OC(O)O—CH₂CF₂H, CH₃—OC(O)O—CH₂CF₃, CH₃—OC(O)O—CH₂CF₂CF₂H,HCF₂CH₂—OCOO—CH₂CH₃, CF₃CH₂—OCOO—CH₂CH₃, or mixtures thereof.

In some embodiments, the electrolyte component of the electrolytecomposition disposed in the housing comprises a fluorinated acyclicether, and the fluorinated acyclic ether comprises HCF₂CF₂CH₂—O—CF₂CF₂Hor HCF₂CH₂—O—CF₂CF₂H.

The housing may be any suitable container to house the electrochemicalcell components. Housing materials are well-known in the art and caninclude, for example, metal and polymeric housings. While the shape ofthe housing is not particularly important, suitable housings can befabricated in the shape of a small or large cylinder, a prismatic case,or a pouch. The anode and the cathode may be comprised of any suitableconducting material depending on the type of electrochemical cell.Suitable examples of anode materials include without limitation lithiummetal, lithium metal alloys, lithium titanate, aluminum, platinum,palladium, graphite, transition metal oxides, and lithiated tin oxide.Suitable examples of cathode materials include without limitationgraphite, aluminum, platinum, palladium, electroactive transition metaloxides comprising lithium or sodium, indium tin oxide, and conductingpolymers such as polypyrrole and polyvinylferrocene.

The porous separator serves to prevent short circuiting between theanode and the cathode. The porous separator typically consists of asingle-ply or multi-ply sheet of a microporous polymer such aspolyethylene, polypropylene, polyamide, polyimide or a combinationthereof. The porous separator may alternatively comprise a substratelayer at least partially coated with a fluorinated polymer. The poresize of the porous separator is sufficiently large to permit transportof ions to provide ionically conductive contact between the anode andthe cathode, but small enough to prevent contact of the anode andcathode either directly or from particle penetration or dendrites whichcan form on the anode and cathode. Examples of porous separatorssuitable for use herein are disclosed in U.S. application Ser. No.12/963,927 (filed 9 Dec. 2010, U.S. Patent Application Publication No.2012/0149852, now U.S. Pat. No. 8,518,525).

Many different types of materials are known that can function as theanode or the cathode. In some embodiments, the cathode can include, forexample, cathode electroactive materials comprising lithium andtransition metals, such as LiCoO₂, LiNiO₂, LiMn₂O₄,LiCo_(0.2)Ni_(0.2)O₂, LiV₃O₈, LiNi_(0.5)Mn_(1.5)O₄; LiFePO₄, LiMnPO₄,LiCoPO₄, and LiVPO₄F. In other embodiments, the cathode active materialscan include, for example:

Li_(a)CoG_(b)O₂ (0.90≤a≤1.8, and 0.001≤b≤0.1);

Li_(a)Ni_(b)Mn_(c)Co_(d)R_(e)O_(2-f)Z_(f) where 0.8≤a≤1.2, 0.1≤b≤0.9,

0.0≤c≤0.7, 0.05≤d≤0.4, 0≤e≤0.2, wherein the sum of b+c+d+e is about 1,and 0≤f≤0.08;

Li_(a)A_(1-b),R_(b)D₂ (0.90≤a≤1.8 and 0≤b≤0.5);

Li_(a)E_(1-b)R_(b)O_(2-c)D_(e) (0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05);

Li_(a)Ni_(1-b-c)Co_(b)R_(c)O_(2-d)Z_(d) where 0.9≤a≤1.8, 0≤b≤0.4,0≤c≤0.05, and 0≤d≤0.05;

Li_(1+z)Ni_(1-x-y)Co_(x)Al_(y)O₂ where 0<x<0.3, 0<y<0.1, and 0<z<0.06.

In the above chemical formulas A is Ni, Co, Mn, or a combinationthereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or acombination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or acombination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, Zr, Ti, arare earth element, or a combination thereof; Z is F, S, P, or acombination thereof. Suitable cathodes include those disclosed in U.S.Pat. Nos. 5,962,166; 6,680,145; 6,964,828; 7,026,070; 7,078,128;7,303,840; 7,381,496; 7,468,223; 7,541,114; 7,718,319; 7,981,544;8,389,160; 8,394,534; and 8,535,832, and the references therein. By“rare earth element” is meant the lanthanide elements from La to Lu, andY and Sc.

In another embodiment, the cathode material is an NMC cathode; that is,a LiNiMnCoO cathode, more specifically, cathodes in which the atomicratio of Ni:Mn:Co is 1:1:1 (Li_(a)Ni_(1-b-c)Co_(b)R_(c)O_(2-d)Z_(d)where 0.98≤a≤1.05, 0≤d≤0.05, b=0.333, c=0.333, where R comprises Mn) orwhere the atomic ratio of Ni:Mn:Co is 5:3:2(Li_(a)Ni_(1-b-c)Co_(b)R_(c)O_(2-d)Z_(d) where 0.98≤a≤1.05, 0≤d≤0.05,c=0.3, b=0.2, where R comprises Mn).

In another embodiment, the cathode comprises a material of the formulaLi_(a)Mn_(b)J_(c)O₄Z_(d), wherein J is Ni, Co, Mn, Cr, Fe, Cu, V, Ti,Zr, Mo, B, Al, Ga, Si, Li, Mg, Ca, Sr, Zn, Sn, a rare earth element, ora combination thereof, Z is F, S, P, or a combination thereof, and0.9≤a≤1.2, 1.3≤b≤2.2, 0≤c≤0.7, 0≤d≤0.4.

In another embodiment, the cathode in the electrochemical cell orlithium ion battery disclosed herein comprises a cathode active materialexhibiting greater than 30 mAh/g capacity in the potential range greaterthan 4.6 V versus a Li/Li⁺ reference electrode. One example of such acathode is a stabilized manganese cathode comprising alithium-containing manganese composite oxide having a spinel structureas cathode active material. The lithium-containing manganese compositeoxide in a cathode suitable for use herein comprises oxides of theformula Li_(x)Ni_(y)M_(z)Mn_(2-y-z)O_(4-d), wherein x is 0.03 to 1.0; xchanges in accordance with release and uptake of lithium ions andelectrons during charge and discharge; y is 0.3 to 0.6; M comprises oneor more of Cr, Fe, Co, Li, Al, Ga, Nb, Mo, Ti, Zr, Mg, Zn, V, and Cu; zis 0.01 to 0.18; and d is 0 to 0.3. In one embodiment in the aboveformula, y is 0.38 to 0.48, z is 0.03 to 0.12, and d is 0 to 0.1. In oneembodiment in the above formula, M is one or more of Li, Cr, Fe, Co andGa. Stabilized manganese cathodes may also comprise spinel-layeredcomposites which contain a manganese-containing spinel component and alithium rich layered structure, as described in U.S. Pat. No. 7,303,840.

In another embodiment, the cathode comprises a composite materialrepresented by the structure of Formula:x(Li_(2-w)A_(1-v)Q_(w+v)O_(3-e))·(1-x)(Li_(y)Mn_(2-z)M_(z)O_(4-d))wherein:

x is about 0.005 to about 0.1;

A comprises one or more of Mn or Ti;

Q comprises one or more of Al, Ca, Co, Cr, Cu, Fe, Ga, Mg, Nb, Ni, Ti,V, Zn, Zr or Y;

e is 0 to about 0.3;

v is 0 to about 0.5.

w is 0 to about 0.6;

M comprises one or more of Al, Ca, Co, Cr, Cu, Fe, Ga, Li, Mg, Mn, Nb,Ni, Si, Ti, V, Zn, Zr or Y;

d is 0 to about 0.5;

y is about 0 to about 1; and

z is about 0.3 to about 1; and

wherein the Li_(y)Mn_(2-z)M_(z)O₄-d component has a spinel structure andthe Li_(2-w)Q_(w+v)A_(1-v)O_(3-e) component has a layered structure.

In another embodiment, in the Formulax(Li_(2-w)A_(1-v)Q_(w+v)O_(3-e))·(1-x)(Li_(y)Mn_(2-z)M_(z)O_(4-d))x is about 0 to about 0.1, and all ranges for the other variables are asstated herein above.

In another embodiment, the cathode in the lithium ion battery disclosedherein comprisesLi_(a)A_(1-x)R_(x)DO_(4-f)Z_(f),wherein:

A is Fe, Mn, Ni, Co, V, or a combination thereof;

R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, Zr, Ti, a rare earth element, ora combination thereof;

D is P, S, Si, or a combination thereof;

Z is F, Cl, S, or a combination thereof;

0.8≤a≤2.2;

0≤x≤0.3; and

0≤f≤0.1.

In another embodiment, the cathode in the lithium ion battery oreelectrochemical cell disclosed herein comprises a cathode activematerial which is charged to a potential greater than or equal to about4.1 V, or greater than or equal to 4.35 V, or greater than 4.5 V, orgreater than or equal to 4.6 V versus a Li/Li⁺ reference electrode.Other examples are layered-layered high-capacity oxygen-release cathodessuch as those described in U.S. Pat. No. 7,468,223 charged to uppercharging potentials above 4.5 V.

In some embodiments, the cathode comprises a cathode active materialexhibiting greater than 30 mAh/g capacity in the potential range greaterthan 4.6 V versus a Li/Li⁺ reference electrode, or a cathode activematerial which is charged to a potential greater than or equal to 4.35 Vversus a Li/Li⁺ reference electrode.

A cathode active material suitable for use herein can be prepared usingmethods such as the hydroxide precursor method described by Liu et al(J. Phys. Chem. C 13:15073-15079, 2009). In that method, hydroxideprecursors are precipitated from a solution containing the requiredamounts of manganese, nickel and other desired metal(s) acetates by theaddition of KOH. The resulting precipitate is oven-dried and then firedwith the required amount of LiOH.H₂O at about 800 to about 1000° C. inoxygen for 3 to 24 hours. Alternatively, the cathode active material canbe prepared using a solid phase reaction process or a sol-gel process asdescribed in U.S. Pat. No. 5,738,957 (Amine).

A cathode, in which the cathode active material is contained, suitablefor use herein may be prepared by methods such as mixing an effectiveamount of the cathode active material (e.g. about 70 wt % to about 97 wt%), a polymer binder, such as polyvinylidene difluoride, and conductivecarbon in a suitable solvent, such as N-methylpyrrolidone, to generate apaste, which is then coated onto a current collector such as aluminumfoil, and dried to form the cathode.

An electrochemical cell or lithium ion battery as disclosed hereinfurther contains an anode, which comprises an anode active material thatis capable of storing and releasing lithium ions. Examples of suitableanode active materials include, for example, lithium alloys such aslithium-aluminum alloy, lithium-lead alloy, lithium-silicon alloy, andlithium-tin alloy; carbon materials such as graphite and mesocarbonmicrobeads (MCMB); phosphorus-containing materials such as blackphosphorus, MnP₄ and CoP₃; metal oxides such as SnO₂, SnO and TiO₂;nanocomposites containing antimony or tin, for example nanocompositescontaining antimony, oxides of aluminum, titanium, or molybdenum, andcarbon, such as those described by Yoon et al (Chem. Mater. 21,3898-3904, 2009); and lithium titanates such as Li₄Ti₅O₁₂ and LiTi₂O₄.In one embodiment, the anode active material is lithium titanate orgraphite. In another embodiment, the anode is graphite.

An anode can be made by a method similar to that described above for acathode wherein, for example, a binder such as a vinyl fluoride-basedcopolymer is dissolved or dispersed in an organic solvent or water,which is then mixed with the active, conductive material to obtain apaste. The paste is coated onto a metal foil, preferably aluminum orcopper foil, to be used as the current collector. The paste is dried,preferably with heat, so that the active mass is bonded to the currentcollector. Suitable anode active materials and anodes are availablecommercially from companies such as Hitachi, NEI Inc. (Somerset, N.J.),and Farasis Energy Inc. (Hayward, Calif.).

The electrochemical cell as disclosed herein can be used in a variety ofapplications. For example, the electrochemical cell can be used for gridstorage or as a power source in various electronically powered orassisted devices (“Electronic Device”) such as a computer, a camera, aradio, a power tool, a telecommunications device, or a transportationdevice (including a motor vehicle, automobile, truck, bus or airplane).The present disclosure also relates to an electronic device, atransportation device, or a telecommunication device comprising thedisclosed electrochemical cell.

In another embodiment, there is provided a method for forming anelectrolyte composition by combining the components described herein.For example, in one embodiment, the method comprises combining at leastone electrolyte component comprising a cyclic carbonate, at least oneadditive comprising a 6-member ring heterocyclic sulfate represented byFormula (I):

wherein n=1, and R¹⁵ to R¹⁸ each independently represent a hydrogen or avinyl (H₂C═CH—), allyl (H₂C═CH—CH₂—), acetylenic (HC≡C—), propargyl(HC≡C—CH₂—), or C₁-C₃ alkyl group, wherein the vinyl, allyl, acetylenic,propargyl, or C₁-C₃ alkyl groups may each be unsubstituted or partiallyor totally fluorinated; and at least one electrolyte salt.

The components can be combined in any suitable order. The step ofcombining can be accomplished by adding the individual components of theelectrolyte composition sequentially or at the same time. After theformation of the first solution, an amount of the electrolyte salt isadded to the first solution in order to produce the electrolytecomposition having the desired concentration of electrolyte salt, andthen the desired amount of the electrolyte component is added.Typically, the electrolyte composition is stirred during and/or afterthe addition of the components in order to form a homogeneous mixture.

EXAMPLES

The concepts disclosed herein are illustrated in the following Examples,which are not intended to be used or interpreted as a limitation of thescope of the claims unless this intention is expressly stated. From theabove discussion and these Examples, one skilled in the art canascertain the essential characteristics of the concepts disclosedherein, and without departing from the spirit and scope thereof, canmake various changes and modifications to adapt to various uses andconditions.

The meaning of abbreviations used is as follows: “° C.” means degreesCelsius; “g” means gram(s), “mg” means milligram(s), “g” meansmicrogram(s), “L” means liter(s), “mL” means milliliter(s), “μL” meansmicroliter(s), “mol” means mole(s), “mmol” means millimole(s), “M” meansmolar concentration, “wt %” means percent by weight, “mm” meansmillimeter(s), “μm” means micrometer(s), “ppm” means parts per million,“h” means hour(s), “min” means minute(s), “psig” means pounds per squareinch gauge, “kPa” means kiloPascal(s), “A” means amperes, “mA” meanmilliampere(s), “mAh/g” mean milliamperes hour(s) per gram, “V” meansvolt(s), “xC” refers to a constant current which is the product of x anda current in A which is numerically equal to the nominal capacity of thebattery expressed in Ah, “rpm” means revolutions per minute, “NMR” meansnuclear magnetic resonance spectroscopy, “GC/MS” means gaschromatography/mass spectrometry, “Ex” means Example and “Comp. Ex”means Comparative Example.

Example 1

The following Example shows room temperature stability of 1,3 propylenesulfate formulations in 1 M LiPF₆, 75 wt % 2,2 difluoroethyl acetate(hereafter “DFEA”), 25 wt % fluoroethylene carbonate (FEC) with LiBOBand maleic anhydride (MA). The resulting formulation for this Examplespecifically comprises 1 M LiPF₆ with 75 wt % DFEA+25 wt % FEC, based onthe weight of DFEA and FEC, +0.85 wt % LiBOB+1.5 wt % 1,3 propylenesulfate+0.5 wt % MA, based on the weight of the total formulation.

Electrolyte Preparation: Preparation of 2,2-Difluoroethyl Acetate (DFEA)

The 2,2-difluoroethyl acetate used in the following Examples wasprepared by reacting potassium acetate with HCF₂CH₂Br. The following isprocedure used for the preparation.

Potassium acetate (Aldrich, Milwaukee, Wis., 99%) was dried at 100° C.under a vacuum of 0.5-1 mm of Hg (66.7-133 Pa) for 4 to 5 h. The driedmaterial had a water content of less than 5 ppm, as determined by KarlFischer titration. In a dry box, 212 g (2.16 mol, 8 mol % excess) of thedried potassium acetate was placed into a 1.0-L, 3 neck round bottomflask containing a heavy magnetic stir bar. The flask was removed fromthe dry box, transferred into a fume hood, and equipped with athermocouple well, a dry-ice condenser, and an additional funnel.

Sulfolane (500 mL, Aldrich, 99%, 600 ppm of water as determined by KarlFischer titration) was melted and added to the 3 neck round bottom flaskas a liquid under a flow of nitrogen. Agitation was started and thetemperature of the reaction medium was brought to about 100° C.HCF₂CH₂Br (290 g, 2 mol, E.I. du Pont de Nemours and Co., 99%) wasplaced in the addition funnel and was slowly added to the reactionmedium. The addition was mildly exothermic and the temperature of thereaction medium rose to 120-130° C. in 15-20 min after the start of theaddition. The addition of HCF₂CH₂Br was kept at a rate which maintainedthe internal temperature at 125-135° C. The addition took about 2-3 h.The reaction medium was agitated at 120-130° C. for an additional 6 h(typically the conversion of bromide at this point was about 90-95%).Then, the reaction medium was cooled down to room temperature and wasagitated overnight. Next morning, heating was resumed for another 8 h.

At this point the starting bromide was not detectable by NMR and thecrude reaction medium contained 0.2-0.5% of 1,1-difluoroethanol. Thedry-ice condenser on the reaction flask was replaced by a hose adapterwith a Teflon® valve and the flask was connected to a mechanical vacuumpump through a cold trap (−78° C., dry-ice/acetone). The reactionproduct was transferred into the cold trap at 40-50° C. under a vacuumof 1-2 mm Hg (133 to 266 Pa). The transfer took about 4-5 h and resultedin 220-240 g of crude HCF₂CH₂OC(O)CH₃ of about 98-98.5% purity, whichwas contaminated by a small amount of HCF₂CH₂Br (about 0.1-0.2%),HCF₂CH₂OH (0.2-0.8%), sulfolane (about 0.3-0.5%) and water (600-800ppm). Further purification of the crude product was carried out usingspinning band distillation at atmospheric pressure. The fraction havinga boiling point between 106.5-106.7° C. was collected and the impurityprofile was monitored using GC/MS (capillary column HP5MS, phenyl-methylsiloxane, Agilent 19091S-433, 30. m, 250 μm, 0.25 μm; carrier gas—He,flow rate 1 mL/min; temperature program: 40° C., 4 min, temp. ramp 30°C./min, 230° C., 20 min). Typically, the distillation of 240 g of crudeproduct gave about 120 g of HCF₂CH₂OC(O)CH₃ of 99.89% purity, (250-300ppm H₂O) and 80 g of material of 99.91% purity (containing about 280 ppmof water). Water was removed from the distilled product by treatmentwith 3 A molecular sieves, until water was not detectable by KarlFischer titration (i.e., <1 ppm).

LiBOB Purification: Lithium Bis(Oxalate)Borate Purification (LiBOB)

In a nitrogen purged dry box, lithium bis(oxalato)borate (LiBOB, SigmaAldrich, 757136-25G) was purified using the following procedure. 25grams of LiBOB was added to a 500 mL Erlenmeyer flask equipped with aTeflon-coated stir bar. To this, 125 mL of anhydrous acetonitrile (SigmaAldrich, Fluka, molecular sieves) was added. The flask was heated at 45°C. for 10 minutes using an oil bath. The mixture was filtered through afine-pore glass frit (Chemglass, F, 60 mL) into a 500 mL filter flaskwith the use of vacuum.

The solution was allowed to cool to room temperature, forming a clearsolution, and 125 mL of cold toluene (Freezer @ −25° C., Sigma AldrichCHROMASOLV®) was added. Immediate precipitation was observed and thismixture was allowed to sit for 20 minutes to allow additional solidformation. The solution was filtered through a fine-pore glass frit(Chemglass, F, 60 mL) into a 500 mL round bottom. The filter cake waswashed with cold anhydrous toluene (2×20 mL) and using a glass funnel,transferred to a cylindrical long neck flask. This flask was cappedtightly, removed from the glove box, and attached to a Kugelrohr, whichwas subsequently attached to a high vacuum. This flask was dried underhigh vacuum (60-100 millitorr) at room temperature overnight, and thenat 140° C. under high vacuum (60-80 millitorr) for an additional threedays. At this time, the flask was capped and returned to the dry box forfurther purification. Propylene carbonate was used to further purify theLiBOB, as described below.

Propylene Carbonate Purification (for Use to Purify LiBOB)

Propylene carbonate (PC, Aldrich, CHROMASOLV for HPLC, 99.7%) wastransferred to the dry box and activated molecular sieves were added.300 mL PC was added to a round bottom flask with a stir bar. This wasattached to a single piece distillation apparatus with a Vigreux column.The apparatus was then put under high vacuum (˜500 millitorr), and thesolution was degassed with stirring. The temperature was then increasedto 50° C., and then 90° C. Eventually, the vacuum increased to ˜250millitorr, and the PC fraction began to distill over. Seven fractionswere collected. The last two fractions (totaling ˜290 mL) were used forfurther purification.

A sacrificial portion of LiBOB was used to trap any remaining impuritiesin the fractionally distilled propylene carbonate. 10.2 g of LiBOB(Rockwood Lithium, Frankfurt, Germany) was combined with 200 mL of thedistilled PC. This was stirred overnight in the dry box, at 100° C. Themixture was then attached to a simple distillation apparatus, and the PCwas distilled off and collected into a round bottom flask. A heat gunwas used multiple times to help the PC distill over. This collected PCwas then transferred to the dry box and used to purify LiBOB.

Purification of LiBOB

In the glove box, to a 250 mL round bottom flask equipped with a Tefloncoated stir bar, 17 g of LiBOB (previously purified using acetonitrileand toluene, as described above) and 75 mL of purified propylenecarbonate were added. This mixture was stirred at room temperature inthe glove box for ˜2 hours. The temperature was increased to 60° C. andstirred for ˜15 minutes.

This tubing was then attached to a simple distillation apparatus. Thedistillation apparatus was sealed using a receiver round bottom flak andclamped rubber tubing. The apparatus was then removed from the dry box.The rubber tubing was attached to the schlenk line/high vacuum, and theapparatus was put under vacuum (˜150 millitorr). The receiver flask wassurrounded by a dry ice/acetone trap, and the LiBOB/PC flask was heatedin an oil bath (55-70° C.). The temperature was adjusted based on theefficiency of the high vacuum. If the temperature is too high, the LiBOBwill start to collect in the top of the distillation head. After most ofthe PC was removed, a heat gun was used to help droplets move from thedistillation head. This was repeated until no droplets appeared. The dryice/acetone receiver trap was then replaced by a liquid nitrogen trap,and the oil bath temperature was slowly increased to 115-130° C. (againdepending on the vacuum). A heat gun was again used to remove dropletsof PC in the distillation head. This was repeated until no more PC wasbeing removed.

The apparatus was then removed from heat/liquid nitrogen and put undernitrogen. After the LiBOB had cooled, and the PC had warmed to roomtemperature, the apparatus tubing was then clamped using forceps to keepit under nitrogen. It was then transferred to the dry box by purging theantechamber with a continuous flow of nitrogen for ˜20 minutes.

ES (Ethylene Sulfate) Purification

In the glove box, 12 g of ethylene sulfate (Chemlmpex, Wood Dale, Ill.)was added to a sublimator equipped with an insert for dry ice/acetone.This was sealed in the dry box, removed, and attached to the high vacuum(˜100 millitorr). The tubing was first put under vacuum before the valvewas opened to put the sublimator under vacuum. The insert was filledwith dry ice and acetone and the bottom of the sublimator was submergedin an oil bath, preheated to 60° C. This was heated for ˜4 hours, oruntil all of the white solid adhered to the cold finger. At this time,the valve was sealed to keep the contents under vacuum. The tubing wasput under nitrogen and removed. The dry ice/acetone trapped was thenemptied, and the outside of the sublimator was cleaned off. This wastransferred into the glove box, and the white solid was collected into adried glass container using a plastic funnel. An NMR of the ES in CDCl3was then obtained to confirm the purity of the additive, and the glasscontainer was stored in the freezer until needed.

MA (Maleic Anhydride) Purification

In the glove box, 27 g of maleic anhydride (Aldrich, Milwaukee, Wis.)was added to a large sublimator equipped with an insert for dryice/acetone. This was sealed in the dry box, removed, and attached tothe high vacuum (˜100 millitorr). The tubing was first put under vacuumbefore the valve was opened evacuate the sublimator. The insert wasfilled with dry ice and acetone and the bottom of the sublimator wassubmerged in an oil bath, preheated to 60° C. This was heated for onehour, and then the temperature was increased to 85° C. for another 7hours, or until all of the sublimed white solid adhered to the coldfinger. At this time, the valve was sealed to keep the contents undervacuum. The tubing was put under nitrogen and removed. The material inthe dry ice/acetone trap was then emptied, and the outside of thesublimator was cleaned off. This was transferred into the glove box, andthe white solid was collected into a dried glass container using aplastic funnel. An NMR of the MA in CDCl3 was then obtained to verifypurity, and the glass container was stored in the dry box until needed.

1,3 Propylene Sulfate Purification

In the glove box, 5 g of 1,3-propylene sulfate (Aldrich, Milwaukee,Wis.) was added to a small sublimator equipped with an insert for dryice/acetone. This was sealed in the dry box, removed, and attached tothe high vacuum (˜100 millitorr). The tubing was first put under vacuumbefore the valve was opened to put the sublimator under vacuum. Theinsert was filled with dry ice and acetone and the bottom of thesublimator was submerged in an oil bath, preheated to 30° C. Thetemperature was increased to 45° C. after 6 hours. After approximatelyeight hours, the material was isolated under vacuum and the oil bath wasturned off for approximately 15 hours. Heating under vacuum resumed, andthe sublimator was heated to 45° C. for eight additional hours. This wasthen removed from high vacuum and transferred to N2 purged dry box forsubsequent handling. An NMR was obtained using CD2Cl2 to confirm productpurity.

Preparation of Electrolyte

The electrolyte was prepared by combining 2,2-difluoroethyl acetate withfluoroethylene carbonate (FEC, BASF, Independence, Ohio) in a 3:1 weightratio in a nitrogen purged dry box. Molecular sieves (3 A) were addedand the mixture was dried to less than 1 ppm water and filtered througha 0.25 micron PTFE syringe filter.

2.0176 g of the mixture described above was combined with 0.0229 g ofLiBOB. The material was gently agitated to dissolve components. 0.0356 g1,3-propylene sulfate, 0.0113 g of MA, and 0.2556 g of LiPF₆ (BASF,Independence, Ohio) were added. The material was placed was gentlyagitated to dissolve the components and prepare the final formulation.

The room Temperature stability of the 1,3 propylene sulfate showed novisible change in color after aging for five weeks at room temperature(25° C.).

NMR samples were prepared in Norell® natural quartz 5 mm tubes, byfilling to with ˜0.6 mL of aged electrolyte sample.

1H and 19F NMR data were used to determine the concentration ofcomponents in the electrolyte formulation. An oxygenated product of FECwas used as an indicator of the extent of reaction of the cyclic sulfateand FEC, and therefore the stability of the formulation at roomtemperature. The amount of oxygenated FEC was calculated as a molepercentage of the entire sample composition. Proton and fluorine NMRspectra were used to determine relative integrals for sample speciespresent.

Proton and fluorine NMR were collected at 500 MHz on a Varian Inova NMR,using a 5 mm HF {C} probe with low fluorine background. Samples wereanalyzed at 27° C. as neat material in 5 mm quartz tubes and wereprepared in a dry box; upon removal from the dry box, samples werequickly placed in the magnet under N₂ flow to avoid potential forexposure to moisture. A standard sample of 50% DMSO-d6, 50% electrolyteof similar composition was first run to set the reference frequency (onescan, proton NMR). Proton or fluorine gradient shimmaps were used toshim the neat samples, and samples were run unlocked. The probe wasdouble-tuned to proton and fluorine simultaneously, slightly favoringfluorine. Receiver gain was adjusted as needed, often setting slightlybelow the value selected by the software's automatic gain routine.

Proton NMR: 128 transients (or scans) were collected using a spectralwindow of 8998.9 Hz, acquisition time of 4.67 s, relaxation delay of 30s, 84058 number of points collected, transmitter offset at −156.9 Hz,pulse-width of 1 s at 57 dB (approximately 15-degree pulse), unlockedwith solvent reference set to DMSO. Spectra were processed with LB of0.5 Hz and zero-filled out to 128 k points.

Fluorine NMR: 1200 transients (or scans) were collected using a spectralwindow of 149253.7 Hz, acquisition time of 1.67 s, relaxation delay of9.3 s, 498508 number of points collected, transmitter offset at −9568.4Hz, pulse-width corresponding to 30-degree pulse (90-degree pulse-widthmeasured for each sample), block size of 4, unlocked with solventreference set to DMSO. Spectra were processed with LB of 2 Hz andzero-filled out to 512 k points.

The fluorine spectra are referenced with respect to chemical shift tothe center resonance of the LiPF₆ doublet at −74.720 ppm, and the protonspectra are referenced with respect to chemical shift to the —CH3singlet of 2,2 difluoroethyl acetate at 2.1358 ppm. In order to quantifythe various electrolyte components, the intensity of the fluorine NMRresonance at −128.25 ppm for 2,2 difluoroethyl acetate was compared withthe proton NMR triplet of triplets at 6.02 ppm to determine acorrelation factor for the proton NMR data. This factor was then appliedto the other species for the proton NMR to scale them to relativeintensities versus the 19F integrals. The 19F multiplet integral at−124.47 ppm and the 1H multiplet integral at 6.40 ppm for FEC were alsoused to double check the correlation factor. Other species which weremeasured by F NMR were the fluorinated phosphate esters, HF anddifluorethanol.

LiBOB was not included in this analysis along with its reactionsproducts, LiF₂BC₂O₄ and LiBF₄.

A doublet of doublets at 6.82 ppm in the proton spectrum was assigned tothe to the —CH(OH)— of the oxygenated FEC molecule. 1H NMR data wasobtained for other additives such as maleic anhydride and 1,3 propylenesulfate, and minor impurities such as propylene carbonate.

For the major components, the error of this analysis was 5-10% relativeto that component. However, for ethylene sulfate and 1,3 propylenesulfate, this error was closer to 10-20% of the component concentrationdue to overlap issues mostly with FEC resonances. However, more accuratedata can be obtained by monitoring the appearance of the oxygenated FECmaterial, which was a reaction product. This value is still accurate towithin 10-20% of the component concentration.

As mentioned above, the oxygenated product of FEC was used as anindicator of the extent of reaction and stability of the formulation atroom temperature. In this case, after aging for five weeks at roomtemperature, the oxygenated product of FEC, 4-hydroxy-1,3-dioxolan-2-onewas very low. A value of 0.0050 mole %, of the entire formulationcomposition, was measured for this species.

After aging for five weeks at room temperature, the formulation did notdevelop any color by visual inspection.

In an embodiment described herein, the electrolyte composition does notshow an oxygenated product of FEC (4-hydroxy-1,3-dioxolan-2-on), above0.01 mole % relative to the entire electrolyte formulation as determinedby NMR, after aging at 25° C. for at least 200 hours, such as up to fiveweeks (840 hours).

Example 2

The following Example describes the preparation of the composition: 1 MLiPF₆+4:21:75 FEC:PC:DFEA (wt %/wt %/wt % based on the total weight ofFEC, PC, and DFEA)+0.85 wt % LiBOB+1.5 wt % 1,3-propylene sulfate+0.5 wt% MA, based on the weight of the total formulation. The electrolyte ofthis Example was prepared by combining 12.8816 g of 2,2-difluoroethylacetate, 0.6821 g of fluoroethylene carbonate (FEC, BASF, Independence,Ohio), and 3.6056 g propylene carbonate (PC, BASF, Independence, Ohio)in a nitrogen purged dry box. Molecular sieves (3 A) were added and themixture was dried to less than 1 ppm water and filtered through a 0.25micron PTFE syringe filter.

1.9991 g of the mixture described above was combined with 0.0233 g ofLiBOB. The material was gently agitated to dissolve components. 0.0351 g1,3-propylene sulfate, 0.0113 g of MA, and 0.2655 g of LiPF₆ (BASF,Independence, Ohio) were added. The material was placed was gentlyagitated to dissolve the components and prepare the final formulation.

Room Temperature Stability of 1,3 propylene sulfate formulations in afluorinated electrolyte formulation containing 4 wt % FEC, 21 wt %propylene carbonate and 75 wt % DFEA (2,2 difluoroethyl acetate) weredetermined by a color change. In this Example, no visible change incolor after five weeks of aging at room temperature.

NMR samples were prepared in Norell® natural quartz 5 mm tubes, byfilling to with ˜0.6 mL of aged electrolyte sample. An oxygenatedproduct of FEC was used as an indicator of the extent of reaction thestability of the formulation at room temperature. The same procedures asdescribed in Example 1 to quantify the concentration of this product,except that propylene carbonate was also measured and quantified in the1H NMR data. In this case, after aging for five weeks at roomtemperature, the oxygenated product of FEC, 4-hydroxy-1,3-dioxolan-2-onewas only 0.00081 mole % of the entire formulation composition.

After aging for five weeks at room temperature, the formulation did notdevelop any color by visual inspection

Comparative Example A

This Example shows room temperature stability of ethylene sulfateformulation: 1 M LiPF₆+4:21:75 FEC:PC:DFEA+0.85 wt % LiBOB+1.5 wt %ethylene sulfate+0.5 wt % MA, versus the same stability properties ofinventive Example 2.

The electrolyte composition 1 M LiPF₆+4:21:75 FEC:PC:DFEA (wt %/wt %/wt% based on the total weight of FEC, PC, and DFEA)+0.85 wt % LiBOB+1.5 wt% ethylene sulfate+0.5 wt % MA, based on the weight of the totalformulation, was prepared by combining 12.8807 g of 2,2-difluoroethylacetate, 0.6879 g of fluoroethylene carbonate (FEC, BASF, Independence,Ohio), and 3.6061 g propylene carbonate (PC, BASF, Independence, Ohio)in a nitrogen purged dry box. Molecular sieves (3 A) were added and themixture was dried to less than 1 ppm water and filtered through a 0.25micron PTFE syringe filter.

5.9997 g of the mixture described above was combined with 0.0620 g ofLiBOB. The material was gently agitated to dissolve components. 0.0350 gof MA and 0.7957 g of LiPF₆ (BASF, Independence, Ohio) were added. Thematerial was placed was gently agitated to dissolve the components.0.1051 g of ethylene sulfate were added right before use, and gentlyagitated to prepare the final formulation. This formulation was allowedto age for 5 weeks before analysis.

After 5 weeks, the following comparison formulation 4:21:75FEC:PC:DFEA+0.85LiBOB+1.5ES+0.5MA, showed visible signs of degradation.Upon visual inspection, it was apparent that the electrolyte changedcolor after aging and now exhibited a yellow tinge.

NMR samples were prepared in Norell® natural quartz 5 mm tubes, byfilling to with ˜0.6 mL of aged electrolyte sample. An oxygenatedproduct of FEC was used as an indicator of the extent of reaction of thecyclic sulfate and FEC and its stability at room temperature. The sameprocedures as described in Example 1 were used to quantify theconcentration of this product, except that the resonances for ethylenesulfate were used instead of 1,3 propylene sulfate in the procedure toquantify the electrolyte components. In addition, propylene carbonate(an electrolyte component) was also quantified in the 1H NMR data.

The NMR of this reaction product showed, compared to Example 2, anincreased level of the oxygenated product of FEC,4-hydroxy-1,3-dioxolan-2-one at 6.8 ppm in the 1H NMR spectrum. In thiscase, the level is approximately 0.026 mole %, which is thirty moretimes greater than what was observed in example 2.

Comparative Example B

This Example shows room temperature stability of ethylene sulfateformulations in 1 M LiPF₆, 75 wt % DFEA, 25 wt % FEC with LiBOB andmaleic anhydride, versus the same stability properties of inventiveExample 1.

The electrolyte composition 1 M LiPF₆ with 75 wt % DFEA+25 wt % FEC,based on the weight of DFEA and FEC, +0.85 wt % LiBOB+1.5 wt % ethylenesulfate+0.5 wt % MA, based on the weight of the total formulation, wasprepared by combining 2,2-difluoroethyl acetate and fluoroethylenecarbonate (FEC, BASF, Independence, Ohio) in a 3:1 weight ratio in anitrogen purged dry box. Molecular sieves (3 A) were added and themixture was dried to less than 1 ppm water and filtered through a 0.25micron PTFE syringe filter.

6.0003 g of the mixture described above was combined with 0.0626 g ofLiBOB. The material was gently agitated to dissolve components. 0.0349 gof MA and 0.7664 g of LiPF₆ (BASF, Independence, Ohio) were added. Thematerial was placed was gently agitated to dissolve the components.0.1048 g of ethylene sulfate were added right before use, and gentlyagitated to prepare the final formulation. This was allowed to age for 5weeks before analysis.

After 5 weeks, the following comparison formulation 1 M LiPF₆ with 75 wt% DFEA+25 wt % FEC+0.85LiBOB+1.5ES+0.5MA, showed visible signs ofdegradation. Upon visual inspection, it was apparent that theelectrolyte changed color after aging and now exhibited a yellow tinge.

NMR samples were prepared in Norell® natural quartz 5 mm tubes, byfilling to with ˜0.6 mL of aged electrolyte sample. An oxygenatedproduct of FEC was used as an indicator of the extent of reaction of thecyclic sulfate and FEC and its stability at room temperature. The sameprocedures as described in example 1 to quantify the concentration ofthis product, except that the resonances for ethylene sulfate were usedinstead of 1,3 propylene sulfate in the procedure quantify theelectrolyte components.

The NMR of this reaction product showed, compared to Example 1, anincreased level of the oxygenated product of FEC,4-hydroxy-1,3-dioxolan-2-one, at 6.8 ppm in the 1H NMR spectrum. In thiscase, the level is approximately 2.2 mole %, which is greater than 400times greater than what was observed in example 1.

Examples 1 and 2 and comparative examples A and B clearly show thatelectrolytes containing sulfates described in this invention are morestable, with respect to reaction with FEC, to electrolytes containingethylene sulfate, and do not discolor after aging at room temperaturefor at least five weeks.

Example 4

This Example describes a solution of 10 weight % of 1,3 propylenesulfate was prepared in FEC. A mixture containing 10 wt % 1,3 propylenesulfate and 90 wt % fluoroethylene carbonate was allowed to age at 25°C. After thirteen days, this solution was slightly colored, but clearlydeveloped much less color than the comparative solution with ethylenesulfate shown below in comparative Example D.

Comparative Example D

A solution of 10 weight % of ethylene sulfate was prepared in FEC. Amixture containing 10 wt % ethylene sulfate and 90 wt % fluoroethylenecarbonate was allowed to age at 25° C. After thirteen days, thissolution was dark brown in color

Example 5

The same procedures to prepare the electrolyte as described in Example 1were used, with the following differences. The electrolyte was preparedby combining 2,2-difluoroethyl acetate with fluoroethylene carbonate(FEC, BASF, Independence, Ohio) in a 3:1 weight ratio in a nitrogenpurged dry box. Molecular sieves (3 A) were added and the mixture wasdried to less than 1 ppm water and filtered through a 0.25 micron PTFEsyringe filter.

5.9998 g of the mixture described above was combined with 0.0705 g ofLiBOB. The material was gently agitated to dissolve components. 0.0350 gof MA, and 0.7688 g of LiPF₆ (BASF, Independence, Ohio) were added. Thematerial was placed was gently agitated to dissolve the components.0.1043 g 1,3-propylene sulfate was added right before use to prepare thefinal formulation.

Comparative Example E

The same procedures to prepare the electrolyte as described in Example 1were used, with the following differences. The electrolyte was preparedby combining 2,2-difluoroethyl acetate with fluoroethylene carbonate(FEC, BASF, Independence, Ohio) in a 3:1 weight ratio in a nitrogenpurged dry box. Molecular sieves (3 A) were added and the mixture wasdried to less than 1 ppm water and filtered through a 0.25 micron PTFEsyringe filter.

9.0204 g of the mixture described above was combined with 0.1042 g ofLiBOB. The material was gently agitated to dissolve components. 0.0520 gof MA, and 1.1503 g of LiPF₆ (BASF, Independence, Ohio) were added. Thematerial was gently agitated to dissolve the components. 0.1566 ofethylene sulfate was then added and the formulation was introduced intothe pouch cell within the next four to 6 hours for electrochemicalevaluation.

A comparison of the performance of Example 5 and Comparative Example Eis shown in the Table below. In this case, the electrolyte containingthe 1,3 propylene sulfate composition showed superior cycle lifeperformance and an increased discharge capacity (at cycle 10) asindicated.

TABLE 1 Cycling Data for Example 5 and Comparative Example E Cycle CapDisc Cy10 Example Electrolyte Description Life 80% mAh/g 5 1M LiPF₆ with75 wt % 339 161 (cell 1) DFEA + 25 wt % FEC/1 wt % LiBOB/1.5 wt % 1.3propylene sulfate/0.5 wt % MA 5 1M LiPF₆ with 75 wt % 453 165 (cell 2)DFEA + 25 wt % FEC/1 wt % LiBOB/1.5 wt % 1.3 propylene sulfate/0.5 wt %MA Comp. E 1M LiPF₆ with 75 wt % 298 158 (cell 1) DFEA + 25 wt % FEC,LiBOB 1 wt % ethylene sulfate 1.5 wt % MA 0.5 wt % Comparative 1M LiPF₆with 75 wt % 303 156 E (Cell 2) DFEA + 25 wt % FEC, LiBOB 1 wt %ethylene sulfate 1.5 wt % MA 0.5 wt %

Pouch Cell Evaluation: Example 5 and Comparative Example E

Pouch Cells

Pouch cells were purchased from Pred Materials (New York, N.Y.) and were200 mAh cells containing an NMC 532 cathode and a graphitic anode.Before use, the pouch cells were dried in the antechamber of a dry boxunder vacuum overnight at 80° C. Approximately 900 microliters of anelectrolyte composition was injected through the bottom, and the bottomedge sealed in a vacuum sealer. For each Example and ComparativeExample, two pouch cells were prepared using the same electrolytecomposition.

Pouch Cell Evaluation Procedure

The cells were placed in fixtures which applied a pressure of 66 kPa tothe electrodes through an aluminum plate fitted with a foam pad. Thecells were held in an environmental chamber (model BTU-433, Espec NorthAmerica, Hudsonville, Mich.) and evaluated using a battery tester(Series 4000, Maccor, Tulsa, Okla.) for the formation procedures (at 25°C.) and the high temperature cycling (at 45° C.). In the followingprocedures, the currents for the C-rates were determined assuming thecell would have a capacity of 170 mAh per g of NMC. Thus currents of0.05 C, 0.25 C, and 1.0 C were implemented in the tester using,respectively, currents of 8.5, 42.5, and 170 mA per gram of NMC in thecell.

The pouch cells were conditioned using the following cycling procedure.In a first cycle, the cell was charged for 36 min at 0.25 C,corresponding to approximately 15% state of charge; this was followed bya four hour rest at open circuit voltage. The first charge was continuedusing constant current (CC) of 0.25 C to 4.35 V. The cell was held at aconstant voltage (CV) at 4.35 V until the current dropped below (ortapered off to) 0.05 C. This was followed by CC discharge at 0.5 C to3.0 V.

For the second cycle, the cell was charged at constant current (CCcharge) of 0.2 C to 4.35 V followed by a CV voltage-hold step at 4.35 Vuntil current dropped below 0.05 C. This was followed by a CC dischargeat 0.2 C to 3.0 V. This cycle was used as a check of the capacity of thecell.

Ten additional cycles were performed using 1C-CCCV protocols whichconsisted of CC charges at 1C to 4.35V, a CV constant voltage step wherethe current was allowed to taper to 0.05 C, followed by a dischargecycle at 1.0 C to 3.0 V.

For the 25° C. formation cycles and the 45° C. cycling described below,the cells also had a 10 min rest following each charge and eachdischarge step. Pressure (66 kPa) was applied to the cells duringformation and cycling, and the cells were evacuated and resealed afterthe final discharge cycle.

Cycling Protocol

The cells were placed in an environmental chamber at 45° C. and cycled:CC charge 1 C to 4.35 V+CV charge to 0.05 C, and CC discharge at 1 C to3.0 V.

The cycle life to 80% capacity retention is the number of cycles neededto reach 80% of the maximum capacity achieved during cycling at 45° C.and is displayed in the table, along with the discharge capacityobserved at cycle 10.

A comparison of the performance of Example 5 and comparative example Eis shown above. In this case, the electrolyte containing the 1,3propylene sulfate composition showed superior cycle life performance andan increased discharge capacity (at cycle 10) as indicated in the tableabove.

The invention claimed is:
 1. An electrolyte composition comprising: atleast one electrolyte component comprising a cyclic carbonate, whereinsaid cyclic carbonate comprises at least one fluorinated carbonate, andwherein the at least one electrolyte component further comprises afluorinated acyclic carboxylic acid ester; at least one additivecomprising a 6-member ring heterocyclic sulfate represented by Formula(I):

wherein n=1, and R¹⁵ to R¹⁸ each independently represent a hydrogen or avinyl, allyl, acetylenic, propargyl, or C₁-C₃ alkyl group, wherein thevinyl, allyl, acetylenic, propargyl, or C₁-C₃ alkyl groups may each beunsubstituted or partially or totally fluorinated; and at least oneelectrolyte salt.
 2. The electrolyte composition of claim 1, wherein the6-member ring heterocyclic sulfate comprises 1,3 propylene sulfate. 3.The electrolyte composition of claim 1 wherein the fluorinated acycliccarboxylic acid ester comprises CH₃—COO—CH₂CF₂H, CH₃CH₂—COO—CH₂CF₂H,F₂CHCH₂—COO—CH₃, F₂CHCH₂—COO—CH₂CH₃, CH₃—COO—CH₂CH₂CF₂H,CH₃CH₂—COO—CH₂CH₂CF₂H, F₂CHCH₂CH₂—COO—CH₂CH₃, CH₃—COO—CH₂CF₃,CH₃CH₂—COO—CH₂CF₂H, CH₃—COO—CH₂CF₃, H—COO—CH₂CF₂H, H—COO—CH₂CF₃, ormixtures thereof.
 4. The electrolyte composition of claim 3, wherein thefluorinated acyclic carboxylic acid ester comprises CH₃—COO—CH₂CF₂H. 5.The electrolyte composition of claim 1, further comprising anon-fluorinated acyclic carbonate.
 6. The electrolyte composition ofclaim 1, wherein the at least one electrolyte component furthercomprises a fluorinated acyclic carbonate.
 7. The electrolytecomposition of claim 6, wherein the fluorinated acyclic carbonatecomprises CH₃—OC(O)O—CH₂CF₂H, CH₃—OC(O)O—CH₂CF₃, CH₃—OC(O)O—CH₂CF₂CF₂H,HCF₂CH₂—OCOO—CH₂CH₃, CF₃CH₂—OCOO—CH₂CH3, or mixtures thereof.
 8. Theelectrolyte composition of claim 7, wherein the fluorinated acycliccarbonate comprises CH₃—OC(O)O—CH₂CF₂H.
 9. The electrolyte compositionof claim 1, wherein the at least one electrolyte component furthercomprises a fluorinated acyclic ether.
 10. The electrolyte compositionof claim 1, further comprising an additive selected from a lithium boroncompound, a cyclic sultone, a cyclic sulfate, a cyclic carboxylic acidanhydride, or combinations thereof.
 11. The electrolyte composition ofclaim 1, wherein said at least one additive comprising a 6-member ringheterocyclic sulfate is present in an amount ranging from 0.1 weightpercent to about 12 weight percent of the total electrolyte composition,sufficient to improve at least one property of the electrolyte chosenfrom (1) battery performance during high temperature cycling conditionsand (2) room temperature stability.
 12. The electrolyte composition ofclaim 1, wherein the electrolyte composition does not show an oxygenatedproduct of FEC (4-hydroxy-1,3-dioxolan-2-on), above 0.01 mole % relativeto the entire electrolyte formulation as determined by NMR, after agingat 25° C. for at least 200 hours.
 13. The electrolyte composition ofclaim 12, wherein the electrolyte composition does not show anoxygenated product of FEC above 0.01 mole % relative to the entireelectrolyte formulation as determined by NMR, after aging at 25° C. fora time ranging from 200-840 hours.
 14. The electrolyte composition ofclaim 1, wherein the cyclic carbonate comprises fluoroethylenecarbonate.
 15. An electrochemical cell comprising: (a) a housing; (b) ananode and a cathode disposed in the housing and in ionically conductivecontact with one another; (c) an electrolyte composition comprising: atleast one electrolyte component comprising a cyclic carbonate, whereinsaid cyclic carbonate comprises at least one fluorinated carbonate, andwherein the at least one electrolyte component further comprises afluorinated acyclic carboxylic acid ester; and at least one additivecomprising a 6-member ring heterocyclic sulfate represented by Formula(I):

wherein n=1, and R¹⁵ to R¹⁸ each independently represent a hydrogen or avinyl, allyl, acetylenic, propargyl, or C₁-C₃ alkyl group, wherein thevinyl, allyl, acetylenic, propargyl, or C₁-C₃ alkyl groups may each beunsubstituted or partially or totally fluorinated; and at least oneelectrolyte salt, wherein said electrolyte composition is disposed inthe housing and provides an ionically conductive pathway between theanode and the cathode; and (d) a porous separator between the anode andthe cathode.
 16. The electrochemical cell of claim 15, wherein theelectrochemical cell is a lithium ion battery.
 17. The electrochemicalcell of claim 15, wherein the cathode comprises a cathode activematerial exhibiting greater than 30 mAh/g capacity in the potentialrange greater than 4.6 V versus a Li/Li⁺reference electrode, or acathode active material which is charged to a potential greater than orequal to 4.35 V versus a Li/Li⁺reference electrode.
 18. An electronicdevice, transportation device, or telecommunications device, comprisingan electrochemical cell according to claim 15.